The relationship between the effects of UV light and thermal shock on gametes and the viability of early developmental stages in a marine teleost fish, the sea bass (Dicentrarchus labrax L.)

To improve the efficiency of gynogenetic induction, the effects of UV light and thermal shock on gametes were investigated in the sea bass. Exposure o f sperm to UV light (greater than or equal to 15000 erg mm(-2)) reduced the amount of motile spermatozoa, without affecting the duration of motility i n the spermatozoa that remained motile. The Hertwig effect was elicited in eggs fertilized with sperm exposed to greater than or equal to 35000 erg mm (-2) of UV light, indicating the inactivation of the DNA of the spermatozoa while retaining their ability to trigger development. Resulting embryos (2 4 chromosomes; one NOR) exhibited the haploid syndrome and died at hatch. D iploidy was restored in eggs fertilized with irradiated sperm by blocking m eiosis II with a thermal shock (0 +/- 0.5 degrees C for 10 min, starting 5 min after fertilization). Resulting larvae (similar to 35% survival at hatc hing) had 48 chromosomes, one or two NOR and no paternal chromosome fragmen ts (gynogenetic diploids). In eggs fertilized with sperm not exposed to UV light, the same thermal shock induced 100% triploidy (72 chromosomes; one, two or three NOR), with 70% survival at hatching. Multifactorial ANOVA show ed that, compared to external factors (sperm diluent, UV light and thermal shock), the contribution of broodstock to the viability of the early develo pmental stages was not significant (P > 0.05). Effects of the thermal shock were most evident after fertilization (30.7%) but disappeared (0%) at hatc hing, suggesting that the lower survival of triploids is a consequence of h andling, not of the triploid condition per se. However, effects of UV light increased through development (42.5-69.7%), probably reflecting cumulative deficits in protein synthesis.